The need sometimes arises for multidirectional observation and measurement of an appearance of an object to be inspected for the purpose of quality control or the like in various industrial fields.
FIG. 12 is a diagram showing an example of a conventional method of observing in many directions an object to be inspected. As shown in the figure, when an object to be inspected, having faces 1b, 1c, and 1e and other faces is observed, an external appearance of the object can be grasped by observation in directions toward the front, back, left, right, top and bottom faces, i.e., the six faces. In this example, the direction of observation of the object is changed by suitably moving a reading device 407, thus performing observation in many directions (directions toward the front, back, left, right, top and bottom faces). In the case where observation in many directions is performed by moving one reading device 407, a moving mechanism considerably complicated and highly sophisticated is required for positioning the reading device 407 and great effort and a long time are required for setting the reading device 407.
As an alternative to this method, a method has also been practiced in which an object to be inspected is observed in a direction freely selected and the direction of observation is changed by moving the object to be inspected. This method, however, requires considerable effort and a complicated process for moving and positioning the object to be inspected. Also, there are limits to the working efficiency and the improvement in observation accuracy.
To know the state of filing of applications for patent or the like aimed at simultaneous observation and measurement in many directions, a survey by search in Japan Patent Office Industrial Property Digital Library has been tried.
(I) Search survey 1
    Menu: Publication text search    Search formula: (six faces+multiple faces)*measurement*simultaneous*(image+picture+figure+taking)    Data: Published patent application    Search date: Dec. 18, 2003    Number of hits: 28(II) Search survey 2    Menu: Publication text search    Search formula: (six faces+multiple faces)*observation*simultaneous*(optical+prism)    Data: Published patent application, Examined patent application publication    Search date: Feb. 19, 2004    Number of hits: 4
In the results of these surveys, the one shown as patent document 1 below relates to a technique of grasping the positional relationship between a plurality of objects to be measured; the one shown as patent document 2 relates to use of an arrangement based on a plurality of mirrors for shape measurement in a case where a dead angle occurs (these are the results of search survey 1); and the one shown as patent document 3 relates to a technique for improving the resolution of an optical distance sensor and reducing the secondary light reflection sensitivity of the sensor.    Patent Document 1: Japanese Patent Laid-Open No. 2003-156333, “Distance measuring apparatus and others”, Abstract.    Patent Document 2: Japanese Patent Laid-Open No. 5-322526, “Three dimensional shape measuring apparatus”, Abstract.    Patent Document 3: Japanese Patent Laid-Open No. 5-240607, “Optical distance sensor”, Abstract.